Windows 8 keys not working to setup Windows 8.1

I have Windows 8 (64-bit) on two computers, a Dell desktop and an Acer laptop. I tried entering both product keys into the Windows 8 Product key page referenced in http://answers.microsoft.com/en-us/w...8-e3461a69dd6e and Microsoft says neither product key works. What is going on here? I bought these computers at Costco - why does Microsoft think these keys are "invalid"?